diff --git a/lib/prelude.js b/lib/prelude.js
index ee30929ac..e1743fa5d 100644
--- a/lib/prelude.js
+++ b/lib/prelude.js
@@ -18,8 +18,10 @@
     // Be nice to AMD
     if (typeof define === "function" && define.amd)
         define(["long"], function(Long) {
-            protobuf.util.Long = Long;
-            protobuf.configure();
+            if (Long && Long.fromValue) {
+                protobuf.util.Long = Long;
+                protobuf.configure();
+            }
             return protobuf;
         });